Electroprecipitation of lithium phosphate nanocomposite electrolytes for Li-ion batteries

Among the rechargeable batteries, Lithium-ion batteries (LiBs) are currently the most widely used in applications such as portable electronics or electric vehicles. While years of battery research have steadily improved the LiB performance, the practical limits of today’s LiB technology are being reached. This is in large part due to the use of liquid electrolytes in the form of Li-salt containing organic solvents. Their main issues include severe safety concerns due to the flammability of the organic solvents and the parasitic side-reactions with high energy active materials, thereby limiting battery lifetime and setting limits to the attainable battery energy. Therefore, a dramatic shift in battery design from liquid-electrolyte based to all-solid-state designs is required. Consequently, the need for novel suitable solid-state electrolytes has sparked worldwide research efforts to work towards this goal. To be considered suitable, the materials must provide high enough Li-ion conductivities, comparable to liquid electrolytes, while also being stable against the highly reactive electrode materials.

At imec/KULeuven we have developed nanocomposite electrolytes (nano-SCE) composed of a silica matrix structure with organic salts. In addition, molecular interaction between the silica surface and the organic molecules results in higher ionic conductivity of the nanocomposite than the individual organic salt mixture. In this master thesis topic, you will explore lithium phosphate as a new possible inorganic matrix component. N-doped Li₃PO₄ or LiPON is a well-known solid electrolyte which has very good stability between 0V and 5V, i.e. interesting for high energy active materials. Unfortunately, its conductivity is far too low to be used in large capacity pouch cells, however it can be improved based on a similar idea of ion-conductivity enhancement in nanocomposites. In this regard, the deposition of lithium phosphate thin films on conductive substrates via electroprecipitation is a highly interesting process. The method works by electrogenerating OH^- near the electrode substrate, which causes the precipitation of lithium phosphate on the electrode. By including other components in the bath mixtures, the fabrication of nanocomposites will be explored. Specifically, you will build further on electro-precipitation of Li₃PO₄ method developed before in the team. Once the process is in place, you will fabricate composite thin films including inorganic or organic templates and test the Li-ion conductivity and electrochemical stability using electrochemical and electrical characterization. In addition, you will use Scanning Electron Microscopy for the morphology, Raman/FTIR for chemical information on interactions and Thermal Gravimetric Analysis for thermal stability of the materials. The experimental work will be carried out at imec. A strong chemical and preferably also an electrochemical background are helpful for this topic.